One objective of this study is to delineate the changes in mental status which accompany normal aging from the 6th decades. These will be correlated with computerized analyses of CT scans and EEG power spectra and evoked potentials. This will allow a quantitative correlation of psychological, structural and physiological indices and will provide valuable normative data. The second goal is to investigate the effect of a toxic-metabolic stress, pneumonia, on mental status in the young and old. The exact profile of impairment in the acute confusional state which can accompany this toxic-metabolic stress, the effects of age on the severity and extent of impairment, and the rate of recovery will be investigated quantitatively. The third objective is to evaluate the cognitive impairments that result from psychiatric depression in subjects of different ages. The rate and extent of cognitive dysfunction that occurs before, during and after treatment with the tricyclic antidepressant, desipramine, and the interaction of this with age will be examined. Finally, patients with the diagnosis of presenile and senile dementia of the Alzhemier's type will be treated with lecithin. Patient responses to this cholinergic treatment will be carefully evaluated in relation to the age of onset, the duration of symptoms and the profile of cognitive impairment. In summary, the objective is to study the cognitive changes seen in normal aging, medical disease, psychiatric depression and dementia, to determine whether the elderly are specifically vulnerable to such changes, and to establish the response of cognitive impairment to specific therapy.